Transient Electrical Conductivity Research Articles

Electromagnetic analysis of composite structures subjected to transient magnetic fields

When carbon composites are exposed to a transient electromagnetic field, a rapid temperature increase can be observed due to joule heating from magnetic induction. The electromagnetic induction heating and heat transfer in the composite are anisotropic and concentrated upon the carbon fiber orientation and distribution. In addition, the strength and frequency of transient electromagnetic fields have great influence on the final quality of the composite. A computational model has been developed by solving coupled Maxwell’s and heat transfer equations. The analysis accounts for the three-dimensional transient electromagnetic field and electrical conductivity of the composite material. This paper will illustrate the derived formulation and numerical solution based on finite element methods. The developed code is validated with a 2D closed-form solution. Numerical simulations of a cylinder and a flat laminated plate are conducted to illustrate the computational capability. The induction heating for composite manufacture is also discussed for current Army’s applications.

Estimation of the Properties of Silver Nanoparticle Ink During Laser Sintering via <I>In-Situ</I> Electrical Resistance Measurement

In this work, the in-situ properties of silver nanoparticle ink were estimated during laser sintering process. The silver nanoparticle ink was composed of 34 wt% silver nanoparticles with an average size of approximately 50 nm, and was deposited on a glass substrate via inkjet printing technology. A 532 nm continuous-wave laser was irradiated to the printed ink for 60 s under various laser intensities. During the laser irradiation, the in-situ electrical conductance of the sintered ink was measured to obtain the transient thermal conductivity of the silver nanoparticle ink using the Wiedemann Franz law. The 2-dimensional, transient heat-conduction equation was calculated to obtain the transient temperature of the silver nanoparticle ink. By coupling the calculated temperature with the measured, transient electrical conductance, the transient thermal conductivity of the ink during the laser sintering process was derived in the calculation. The calculated thermal conductivity of the ink sintered at a laser intensity of 467.9 W/cm2 with 598 K is 355.5 W/mK, which is 86.4% of the thermal conductivity of bulk silver, 411.4 W/mK, at that tempearture. The difference resulting from the porosity of the sintered ink has an effect on the thermal conductivity of the sintered ink.

Transient metal-like electrical conductivity in swift heavy ion irradiated insulators

The irradiation of insulators with swift heavy ions leads to a transient excitation of valence band electrons into the targets conduction band. The population of the conduction band gives rise to an increased electrical conductivity of the intrinsically non-conductive insulator. Due to the transient nature of the number density of excited electrons in the conduction band, the electrical conductivity is also strongly time dependent. In this work it is demonstrated how the transient electrical conductivity can be evaluated on the basis of a combination of the Monte Carlo method and a two temperature model. As a model system, the irradiation of SiO2 with 11.4MeV/u Ca ions, corresponding to a stopping power of dE/dx=2.7keV/nm, is chosen for the calculations. It is found, that the enhancement of the electrical conductivity is quite large and comparable to that of metals like gold. The striking magnitude of this enhancement may allow for an experimental measurement of the electrical conductivity of insulators during irradiation with swift heavy ions.

DC conductivity and dielectric properties of maize starch/methylcellulose blend films

The transient current, electrical conductivity, dielectric constant (e′), and dielectric loss factor (e″) of starch and methylcellulose homopolymers and their blends with various compositions were studied under different conditions. The x-ray diffraction pattern was obtained for individual polymers and 50:50 wt/wt% blend sample to identify both the structure and degree of crystallinity. From transient current, the ionic and electronic transfer number as well as charge carrier density and drift mobility were determined. The values of activation energy in the temperature range 30–90 °C indicate that the conduction mechanism is due to combined electronic and ionic processes, while in the temperature range 100–160 °C, electronic contribution is predominant. The complex dielectric data of the present samples in an extended frequency and temperature range appear as different relaxation processes, which are connected with polymer dynamics.

The transient electrical conductivity of W-based electron-beam-induced deposits duringgrowth, irradiation and exposure to air

W-based granular metals have been prepared by electron-beam-induced deposition from the tungstenhexacarbonyl W(CO)6 precursor. In situ electrical conductivity measurements have been performed to monitor thegrowth process and to investigate the behavior of the deposit under electron beampost-irradiation and by exposure to air. During the first part of the growth process, theelectrical conductivity grows nonlinearly, independent of the electron beam parameters. Thisbehavior is interpreted as the result of the increase of the W-particle’s diameter. Once thegrowth process is terminated, the electrical conductivity decreases with the logarithm of time,σ∼ln(t). Temperature-dependent conductivity measurements of the deposits reveal that theelectrical transport takes place by means of electron tunneling either between W-metalgrains or between grains and trap sites in the matrix. After venting the electron microscopethe electrical conductivity of the deposits shows a degradation behavior, which depends onthe composition. Electron post-irradiation increases the electrical conductivity of thedeposits.

Chemical diffusion in molybdenum disulphide

Ceramic molybdenum disulphide (MoS 2) was equilibrated at an ambient sulphur vapour partial pressure p(S 2), 10 Pa< p(S 2)<1000 Pa. After the step change of p(S 2) to a new value, the equilibration kinetics was monitored by measuring electrical conductivity. The application of the solution of Fick's second law (with the initial condition: no concentration gradient in specimen and the boundary condition: surface concentration constant) to the kinetic data gave the chemical diffusion coefficient. The chemical diffusion coefficient, D chem, determined at 1273 K, was D chem=(3.20±0.32)*10 −7 cm 2 s −1 and was found to be independent of sulphur vapour partial pressure. The usefulness of transient electrical conductivity method for determining real values of diffusion data was discussed in terms of defect structure of the studied material.

Modeling and Simulation of Ionic Currents in Three-Dimensional Microfluidic Devices with Nanofluidic Interconnects

Electrokinetic fluid flow in nanocapillary array (NCA) membranes between vertically separated microfluidic channels offers an attractive alternative to using mechanical action to achieve fluidic communication between different regions of lab-on-a-chip devices. By adjusting the channel diameter, a, and the inverse Debye length, к, and applying the appropriate external potential, the nanochannel arrays, can be made to behave like digital fluidic switches, and the movement of molecules from one side of the array to the other side can be controlled. However, inherent differences in ionic mobility lead to non-equilibrium ion populations on the downstream side, which, in turn, shows up through transient changes in the microchannel conductance. Here we describe coupled calculations and experiments in which the electrical properties of a microfluidic–nanofluidic hybrid architecture are simulated by a combination of a compact model for the bulk electrical properties and iterative self-consistent solutions of the coupled Poisson, Nernst–Planck, and Navier–Stokes equations to recover the detailed ion motion in the nanopores. The transient electrical conductivity in the microchannel, after application of a forward bias pulse to the NCA membrane, is recovered in quantitative detail. The surface charge density of the nanopores and the capacitance of the membrane, which are critical determinants of electrokinetic flow through NCA, fall out of the analysis in a natural way, providing a clear mechanism to determine these critically important parameters.

Transport of lanthanum ion and hole in LaCrO 3 determined by electrical conductivity measurements

Effective diffusion coefficient in LaCrO 3 was determined by transient electrical conductivity based on Fick's second law. The diffusion coefficient of La 3+ ion was calculated from the effective diffusion coefficient. The diffusion coefficient of La 3+ ion and the activation energy was in agreement with the reported value. The diffusion coefficient of hole in LaCrO 3 was also calculated from electrical conductivity and hole concentration. The hole concentration is estimated from the relation between the electrical conductivity and the amount of alkaline-earth in (La,A)CrO 3 (A=Sr, Ca). The diffusion coefficient of hole in LaCrO 3 was much higher than those of other components in LaCrO 3.

Transient and AC electrical conductivity of porous silicon thin films

AC impendance spectroscopy measurements as a function of the applied voltage in the range 0.5 V up to 3 V, as well as measurements of the transient current of porous silicon thin films as function of the applied voltage in the range 1V up to 9 V were performed in order to investigate the conduction mechanisms in PS. The analysis of the experimental results shows that within the range of the frequency span and time range the conductivity is attributed to ions in the early stages (up to 10 -3 s) of the applied voltage. The voltage dependence of the ionic conductivity is ohmic. The Poole-Frenkel conduction mechanism prevails following the establishment of high internal electric fields, which occur for times greater than 10 -3 s after the application of the voltage.

Temperature dependence of the transient and AC electrical conductivity of porous silicon thin films

In order to investigate the prevailing conduction mechanisms of porous silicon (PS) thin films AC impedance spectroscopy measurements, as well as transient current measurements, as a function of voltage, were performed in the temperature range from 170 to 350 K. The frequency span was 1 Hz up to 1 MHz and the time range 5×10 −5–10 s. The analysis of the experimental results involved correlation between AC and transient conductivity. The AC and transient conductivity measurements obey the Power Law of Dielectric Universal Response. The analysis shows that, within the range of the frequency span and time range of the measurements, the electrical conductivity is governed by three conduction mechanisms: In the low temperature region, specifically from 170 to 230 K, tunneling is the prevailing conduction mechanism. In the temperature range from 230 to 350 K two more thermally activated mechanisms contribute to the conductivity of PS thin films. The Ohmic conduction mechanism follows tunneling and precedes the Poole–Frenkel conduction mechanism. The time interval within each of these mechanisms is the prevailing one depends on temperature and applied voltage. The activation energy of Ohmic conduction as well as the exponential factor of Poole–Frenkel mechanism have been calculated.

Solute trapping in aluminum alloys

We report the first measurements of solute trapping in metallic alloys. The nonequilibrium solute partition coefficient k was measured in several dilute aluminum alloys (AlCu, AlGe, AlIn, AlSn). Pulsed laser melting was used to bring about rapid plane-front solidification at velocities of 0.6-5.1 m/s. Time-resolved melt depths and solidification velocities were determined using the transient electrical conductance and optical reflectance techniques. The solute trapping model with the fewest free parameters that accounts for the measured velocity dependence of k is the Continuous Growth Model of Aziz and Kaplan. We have also identified an inverse correlation between the diffusive speed (the only free parameter in that model) and the equilibrium partition coefficient; this correlation might be used to estimate diffusive speeds for systems in which it has not been measured. A possible origin of such a correlation is discussed.

Proton Conducting Polymer Electrolytes: Polyethylene Oxide+(NH4)2SO4System

A new proton-conducting polymer electrolyte polyethylene oxide (PEO)+(NH 4 ) 2 SO 4 has been reported. The proton transport in solution-cast films of PEO complexed with (NH 4 ) 2 SO 4 has been established using optical microscopy, XRD, DTA, IR, coulometry, transient ionic current and electrical conductivity studies. The highest electrical conductivity has been found to be 9.3× 10 -7 S · cm -1 for the NH 4 + /EO ratio equal to 0.0416. The transference number and mobility of protonic movement have been found to be t H + ≃0.61 and µ H + ≃2.9×10 -7 cm 2 /volt-sec, respectively. The movement of anions (possibly HSO 4 - ) also contribute to the overall conductivity.

Transient and AC electrical conductivity of potassium chloride and potassium bromide thin films

The transient and AC electrical conduction in KCl and KBr thin films have been studied at room temperature between 0.4 and 2.0 V. The time in the transient study covered the range 10-5 s to 104 s following the application of a step voltage. The frequency range in the AC study was 1 Hz to 200 kHz. From the frequency dependence of the AC conductivity and the application of Fourier transforms a transient current is calculated numerically, which differs from the experimentally determined transient current. Taking into consideration the experimental fact that the systems studied respond linearly to harmonically varying voltages, the observed discrepancies between AC and transient electrical conductivities are attributed to different mechanisms. Specifically the AC conductivity is attributed to hopping anions, whereas the transient conductivity is due not only to hopping anions but also to the release of trapped electrons by overcoming the barrier of the trap (Poole-Frenkel effect) alone or assisted by tunnelling through the barrier.

Proton conducting polymer electrolyte: II poly ethylene oxide + NH4l system

A new proton conducting polymer electrolyte PEO + NH4l system has been investigated. The solution-cast films of different stochiometric ratios have been prepared and characterized. Proton transport has been established using various experimental studies, namely optical microscopy, X-ray diffraction, differential thermal analysis, infrared, coulometry transient ionic current and electrical conductivity measurements at different temperatures and humidity. The maximum conductivity of the complexed material has been found to be ∼10−5 S cm−1. Both H+ ion and I− anion movements are involved with respective transference numbers and mobilities astH+=0.74, ,tl−=0.09, μH+=4.97 × 10−6 cm2 V−1 s−1 and μl−=7.65.

Protonic conduction in Al2(SO4)3·16H2O: coulometry, transient ionic current, infrared and electrical conductivity studies

Proton transport in Al2(SO4)3·16H2O has been established using different techniques namely coulometry, transient ionic current, i.r., DTA/TGA and electrical conductivity. The possible charge carriers are H+ and OH− generated as a result of possible electrolysis of hydrate water molecules. The mobilities of the two charge carriers are approximately 4×10−5 and 2.4×10−5cm2V−1s−1. The electrical conductivity shows strong dependence upon humidity and also shows a against 1/T behaviour closely related with its thermal dehydration reaction.

Protonic conduction in Al2(SO4)3�16H2O: coulometry, transient ionic current, infrared and electrical conductivity studies

Protonic conduction in Al2(SO4)3�16H2O: coulometry, transient ionic current, infrared and electrical conductivity studies

Quasilinear hyperbolic systems and characteristics in transient electrical conduction

Wave propagation is often described by hyperbolic systems of partial differential equations. When such systems are not linear, it is frequently impossible to obtain the analytical form of the characteristic curves of these systems. The author shows that the equations governing the transient electrical conduction in solids constitute a fair example of a quasilinear system where the characteristics describing the propagating wavefronts of electrons and holes can be obtained straightforwardly. This example also exhibits the role of the characteristics as transporters of discontinuities in the partial derivatives of the dependent variables.

Transient and ac electrical conductivity in evaporated thin rubidium bromide films

The transient and ac electrical conduction in thin RbBr films has been studied at room temperature as a function of the applied voltage. The results show that the electrical conductivity is due to hopping anions in the ac conductivity and at early times (10 −5 to 10 −2 s) in the transient conductivity. At times >10 −2 s the transient conductivity is due not only to hopping anions, but to the release of trapped electrons as well, either by overcoming the barrier of the trap (Poole-Frenkel effect) alone or assisted by tunneling through the barrier.

Proton-conducting polymer electrolyte. I. The polyethylene oxide+NH4ClO4 system

Proton transport in solution-cast films of polyethylene oxide (PEO) complexed with ammonium perchlorate (NH4ClO4) has been established using optical microscopy, XRD, DTA, IR, coulometry, transient ionic current and electrical conductivity studies. The solubility of NH4ClO4 in PEO is found to be limited to a maximum concentration NH4+/EO ratio of 0.167. The highest conductivity ( approximately 1.05*10-5 S cm-1) is for the film with NH4+/EO=0.02-0.1. The H+ ion transference number, tH+, and mobility, mu H+, are 0.85 and 1.7*10-4 cm2 V-1 s-1, respectively. The movement of ClO4- ions also contributes slightly to the overall charge transport.

A study on the AC and transient electrical conduction in evaporated thin potassium iodide films

The AC conduction in thin potassium iodide films in the range 5 Hz to 20 kHz has been studied for applied voltages between 0.4 and 1.2 V at room temperature. The universal dielectric response sigma =b omega n for AC conductivity is obeyed for all the applied voltages. Taking into consideration the linearity in the AC conductivity and the nature of the potassium iodide films, previous results on the transient electrical conductivity of thin potassium iodide films are analysed and resolved into two components, one of which is associated with ionic conductivity and the other with the Poole-Frenkel effect.